Resilient plastic piston ring

ABSTRACT

A plastic ring for internal combustion engine pistons. In a preferred embodiment, the ring has a flat outer diameter adapted to engage the inner diameter of a compression piston ring and an inner diameter adapted to engage the backwall of the ring groove. An axial groove slightly spaced from the outer diameter extends into the ring from the top thereof, whereby combustion gases will expand the ring so that it acts as a circumferential expander for the compression ring while preventing blowby of gases through the ring groove. In another modification, the ring is used with its outer diameter acting against the cylinder wall.

Unite 1? States Patent [72] Inventors Herbert F. Prasse Town andCountry; Harold E. McCormick, Ballwin, both of Mo. [2]] Appl. No. 16,278[22] Filed Mar. 4, 1970 [45] Patented Sept. 28,1971 [731 Assignec RamseyCorporation St. Louis, Mo.

[54] RESILKENT PLASTIC PlSTON RHNG 14 Claims, 14 Drawing Figs.

[52] US. Cl 277/58, 277/165, 277/223 [51] 1nt.Cl F16j 9/00, F16j 9/20[50] Field of Search 277/58, 138, 139, 154, 155, 165,216, 223, 224

156] References Cited UNITED STATES PATENTS 2,456,529 12/1948 Naab277/165 Primary Examiner-Robert J. Smith Attorney-Hill, Sherman, Meroni,Gross & Simpson ABSTRACT: A plastic ring for internal combustion enginepistons. In a preferred embodiment, the ring has a Hat outer diameteradapted to engage the inner diameter ofa compression piston ring and aninner diameter adapted to engage the backwall of the ring groove. Anaxial groove slightly spaced from the outer diameter extends into thering from the top thereof, whereby combustion gases will expand the ringso that it acts as a circumferential expander for the compression ringwhile preventing blowby of gases through the ring groove. in anothermodification, the ring is used with its outer diameter acting againstthe cylinder wall.

RESILIENT PLASTIC PISTON RING BACKGROUND OF TH E INVENTION 1. Field ofthe Invention This invention relates to internal combustion engines andmore particularly to a piston ring for use in such engines.

2. Prior Art Recently, more emphasis has been placed upon controllinginternal combustion engine emissions. It has been determined that asignificant quantity of undesirable emissions as well as power loss arethe result of combustion blowby. Such blowby occurs between the outerdiameter of the piston and the cylinder wall. While compression rings,carried by the piston in ring grooves, have been used to seal thisspace, the prior art rings and ringsets do not completely seal thefiring chamber.

Blowby can still occur between the outer diameter of the piston ring andthe cylinder wall, or by a gas flow around the piston ring in the ringgroove. It has been suggested to overcome the first form of blowby byplacing expansion springs in the ring groove to force the piston ringinto tighter contact with the cylinder wall. Such expansion springs,while helpful, increase the friction of the piston ring against thecylinder wall at all times by applying a continuous pressure to theinner diameter of the piston ring.

It has been further suggested that the piston ring be made substantiallyL-shaped, as in the US. Pats. to RS. Moore, No. 1,159,066 and Goetze,No. 2,844,424, with one leg of the L engaging the cylinder wall whilethe other leg is retained in the ring groove. In such constructions, theforce of the entrapped combustion gases is used to expand,circumferentially, the first leg into tighter engagement with thecylinder wall. While such rings may be effective in reducing blowbybetween the ring and the cylinder wall, they are not effective inpreventing the escape of such gas through the ring groove. Further,because such rings are historically of split annular construction, aconsiderable amount of gas can escape in the area of the ring gap.

SUMMARY OF THE INVENTION Our invention overcomes the disadvantages ofthe prior art by providing a resilient plastic piston ring whichutilizes the pressure of the entrapped gas to expand the main pistonring into tighter sealing engagement with the cylinder wall while at thesame time expanding a portion of the ring into greater sealing contactwith the ring groove walls whereby escape is prevented at both theinterface between the piston ring and the cylinder wall and theinterface between the ring and the groove walls. Because the ring reliesupon the pressure of entrapped gas to provide the expansion force,friction is reduced during those portions of the engine cycle whileeither the pressure retained is reduced, as during exhaust, or wherethere is no pressure retained as during intake.

In a preferred embodiment, the ring is slightly U-shaped with one leg ofthe U being radially thinner and axially shorter than the other. Thering is bottomed in the ring groove and is utilized as a backing for astandard piston ring. The opening of the U opens axially upwardly andcompressed gases seeking exit through the ring groove will be forcedinto the bight resulting in a radial expansion of the ring by pressingthe legs of the U further apart. This will at the same time seat thering more firmly against the backwall and bottom wall of the ring groovewhile increasing its expansion pressure against the piston ring.

In another preferred embodiment, the expansion ring has grooves in boththe t op and bottom faces and a circumferential groove in the internaldiameter face. The external diameter face is planar and abuts theinternal diameter of a standard composition piston ring or of a ringpair.

In yet another embodiment, the resilient plastic piston ring of thisinvention is used without a standard piston ring and has its outerdiameter adapted to contact the cylinder wall. The ring is seatedagainst the bottom of the ring groove and is preferably used in a grooveimmediately adjacent the top of the piston to control blowby or may beused in a lower groove, in an inverted position, to function as an oilcontrol ring.

In yet another embodiment, the ring is bottomed in the ring groove andhas a slanted outer diameter face adapted to engage the cylinder wall, aportion of the outer periphery extending below the normal ring groovedepth in a secondary curved cutback groove.

In each instance the ring is preferably made of a high-temperatureresilient plastic such as Vespel (Reg. trademark of E. I. du Pont deNemours & Co. for a polyimide resin), Teflon (Reg. trademark for apolytetrafiuoroethylene manufactured by E. I. du Pont de Nemours & Co.),or one of the high-temperature aromatic polyimides. Although the ring ispreferably a 360 continuous ring, specific materials may require the useof a split ring for specific applications.

In those instances where the plastic ring does not contact the wall ofthe combustion cylinder, in addition to the above mentionedhigh-temperature plastics, a high-temperature fluoroelastomer may beused such as Viton (Reg. trademark of E. I. du Pont de Nemours & Co. fora fluoroelastomer).

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantagesof the invention will be readily apparent from the following descriptionof certain preferred embodiments thereof, taken in conjunction with theaccompanying drawings, although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts of the disclosure, and in which:

FIG. I is a fragmentary crossseetional view of the piston ring of thisinvention illustrating the ring seated in a ring groove behind astandard compression piston ring.

FIG. 2 is a view similar to FIG. I illustrating a different ring used inconnection with a keystone piston ring.

FIG. 3 is atop plan view of a modified piston ring of this in vention.

FIG. 4 is a partially sectional side plan view of the FIG. 3 embodimentof the ring of this invention.

FIG. 5 is a cross-sectional view of the ring of FIG. 3, taken along theline V-V.

FIG. 6 is a fragmentary crosssectional view of the ring of FIGS. 3, 4and 5 received in a piston ring groove and used as an expansion ring fora pair of standard composition piston rings.

FIG. 7 is a fragmentary cross-sectional view of a piston equipped withone of the embodiments of the ring of this invention.

FIG. 8 is a view similar to FIG. 7, illustrating the ring of FIG. 1 asreceived in a piston.

FIG. 9 is a cross-sectional view of the embodiment illustrated in FIG.7.

FIG. 10 is a fragmentary cross-sectional view of the ring area of apiston received in a cylinder, illustrating one embodiment of thecontinuous ring of this invention utilized for blowby control.

FIG. II is a top plan view of the ring illustrated in FIG. 10.

FIG. 12 is a fragmentary enlarged cross-sectional view of the top ringgroove of FIG. 10, illustrating the ring.

FIG. 13 is a fragmentary cross-sectional view of the ring grooves of amodified piston illustrated as received in a cylinder wall and showingother combination uses for the ring of the invention.

FIG. I4 is a fragmentary cross-sectional view of a ring groove of amodified piston received in the cylinder, illustrating anotherembodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 8 fragmentarilyillustrates a piston 20 of the type such as is used in internalcombustion engines, especially diesel engines and the like. The piston20 has a head portion 21 equipped with a plurality of circumferentialgrooves 22, 23, 24 and 25. The grooves receive piston rings whichproject outwardly therefrom to provide a seal between the piston and thecylinder in which the piston is received. The rings may be of thecompression type such as the rings 26, 27, and 28 or may be oil controlrings such as the ring 29.

ln the view illustrated, the ring 26 is illustrated as being a torsiontwist keystone ring received in a wedge-shaped groove, the ring 27 isillustrated as being a conventional rectangular compression ring with acoated wear face received in a rectangular groove 23, and the ring 28 isillustrated as being a bevelled-faced compression ring with a wearcoated face also received in a rectangular groove 24. The oil controlring 29 illustrated is a one-piece U-shaped ring expanded by acircumferentially expanding spring 30.

Although many advances have been made in the design of the piston rings,with the increasing use of high-performance engines and the increasingcombustion pressures encountered therein, conventional piston ringsstill allow a significant amount of combustion gases to escape from thecombustion area by traversing the path between the piston head andcylinder wall. Some of this escapage occurs between the outer diameterof the rings and the cylinder wall. A large amount also occurs bypassage of gas around the piston ring in the ring groove. It is thepurpose of this invention to minimize such gas blowby.

In order to effectuate this purpose, in the embodiment illustrated inFIG. 8, a plastic piston ring 31, according to this invention, is placedin a ring groove behind the conventional piston ring. The ring 31 isillustrated as being placed in the ring groove 23 behind the compressionring 27.

FIG. 1 is an enlarged fragmentary view of the ring groove 23 and rings27 and 31. In accordance with the customary practice, the groove isaxially taller and radially deeper than the conventional piston ring 27so that the ring may be movable therein.

The ring 31 is positioned radially inwardly of the ring 27, and ispreferably bottomed against the backwall 34 of the groove 23. Theradially inner portion 35 of the ring preferably has a axial heightapproximately the same as the axial height of the groove 23. The frontor outer diameter face 36 of the ring rides against the inner diameter37 of the ring 27 and has an axial height less than the axial height ofthe inner diameter portion 35. An axially extending groove 38 projectsinto the ring between the radially outer portion 39 and the radiallyinner portion 35 with the inner portion being slightly thicker in aradial direction than the outer portion.

The groove 38 tapers axially upward and radially outward to a point 40either at or in close-spaced relation to the radially outer face 36. itis to be understood that although the ring 31 is illustrated as havingits radially inner portion 35 thicker than the radially outer face 36.It is to be understood that although the ring 31 is illustrated ashaving its radially inner portion 35 thicker than the radially outerportion 39, the two being separated by the groove 38, that this is amatter of design and that in specific embodiments the thicknesses may bevaried. Further, it is to be understood that the dimensions of the rings31 are set so that it may be inserted into the ring groove behind thecompression ring 27 in such a manner that it will not adversely affectcorrect installation of the ring 27. it will further be understood thatthe ring 31 may be assembled with a clearance relationship between itsinner diameter and the backwall of the groove or between its outerdiameter and the back of the ring 27 so as to allow the ring 27 to becompressed when inserted into the cylinder. In this manner, the normalcircumferential expansion force of the ring 27 against the cylinder wallis preserved.

The ring 31 is constructed of a high-temperature plastic and preferablyof plastics such as the polyimides which are relatively stable at thetemperature encountered-in an internal combustion engine. An acceptableplastic for use in constructing the ring 31 is known as Vespel, aregistered trademark of the du Pont corporation. Such plastics arecapable of continuous operation of temperatures of up to 500 F. andintermittent temperature exposures up to 900 F.

The ring is preferably constructed of material which has an elasticmemory so that the ring may be constructed as a continuous 360 ring.When so constructed, the ring is stretched to be fittable over thepiston head and thereafter shrunk to its normal diameter within the ringgroove. in lower ring groove applications, plastic materials such asTeflon (a registered trademark of the E. l. du Pont de Nemours & Co.)may be utilized. Where the elastic memory of the material is such as tobe undesirable for the stretching and shrink flt insertion into the ringgroove, the ring may be split to facilitate installation. It is to beunderstood that although different materials may be used, the preferredmaterial is a material such as Vespel or Viton. Viton is afluoroelastomer which in commercial embodiments such as Viton A or VitonB exhibits the desired properties of high-temperature stability andflexibility. Further, the material must be resilient at the operatingtemperatures encountered in the ring groove and should haveselflubricating properties.

In the absence of pressure acting on the ring 31, the ring exerts littlecircumferential expansion force against the compression ring 27.However, during combustion, high-pressure gases flow into the ringgroove 23 as illustrated by the arrows 40. The high-pressure gas willflow into the groove 38 where it will act equally against the radiallyinner wall of the groove 42, the radially outer wall of the groove 44and the bight of the groove 43. This action will cause an expansion ofthe resilient material ring by increasing the radial depth of thegroove. ln this manner, the radially inner portion 35 will be pressedinto tighter engagement with the bottom of the ring groove to preventescape of compression gas around the inner diameter of the ring 31. Theaction of the gas against the bight portion 43 of the groove will forcethe ring 31 into tighter sealing engagement with the bottom wall 45 ofthe ring groove, thereby aiding in preventing flow of the compressiongas around the ring 31. The pressure of the gas against the outerdiameter wall 44 of the groove will act to force the outer diameter wall36 of the ring 31 against the inner diameter wall 37 of the compressionring 27. This will create a circumferential expansion force against thecompression ring 27 to increase the sealing pressure between thecompression ring and the cylinder wall. This pressure also increases thesealing pressure between the outer diameter wall 36 of the ring 31 andthe inner diameter wall 37 of the ring 27, thereby preventing flow ofgas between the two rings.

It can therefore be seen that the compression gases will be effectivelytrapped within the ring groove in such a manner that leakage pathswithin the groove are blocked by a sealing force which is proportionateto the pressure of the gas. This will reduce or eliminate blowby throughthe ring groove while at the same time reducing blowby between thecompression ring face and the cylinder wall by increasing the expansiveforce of the compression ring against the cylinder wall in directresponse to the increase of compression gas pressure. Because the ring31 is resilient, it is able to accommodate the radial expansion causedby relative movement between the radially inner portion 35 and theradially outer portion 39. Further, due to its resiliency, when thepressure of the compression gases is reduced, as during the intake cycleof a fourcycle engine, the ring 31 will resume its initial shapereducing circumferential force against the compression ring 27 andthereby lessening friction between the compression ring 27 and thecylinder wall.

FIG. 2 illustrates another embodiment of the ring 31. The ring 51illustrated in FIG. 2 is shown fitted into a wedgeshaped groove 52 whichreceives a keystone ring 53. The ring 51, as the ring 31, is receivedradially inwardly of the compression ring 53. The ring 51 also has acentral axial groove 54 extending into the ring from the top thereof.The radially inner wall 55 ofthe ring 51-is angled axially upward andradially inward to provide a sloping backface. The radially outerdiameter face 56 of the ring is curved to give the ring a barrel facecontour. The combination of the slanting backface 55 and the curvedbarrel face 56 allows the ring 51 to effectively seal the ring groove 52with minimal normal contact between the ring 51 and the walls of thering groove and the inner diameter of the compression ring. Further, dueto the resiliency of the material of the ring 51 and the slanting innerdiameter face 55 and barrel-shaped outer diameter face 56, the ring doesnot exert as large a circumferential expansion force as does the ringillustrated in FIG. 1. Further, some of the force of the compressiongases may be utilized in deforming the inner peripheral portion 57 ofthe ring 51, thereby reducing the space 58 between the slanted face 55and the bottom of the ring groove.

FIGS. 3 through 6 illustrate another embodiment of the plastic pistonring of this invention. The ring 61 has both top 62 and bottom 63 axialgrooves. There is also an inner diameter groove 64 extending radiallyinto the ring from the backface thereof. The outer diameter face 65 isaxially straight and is designed to mate with the inner diameter of aconventional compression ring or rings.

Conventional piston rings have a radial gap therein to allow insertioninto the piston ring groove. Such gaps provide an escape path forcombustion gases. In order to close this gap, it has been suggested toplace two axially thin compression piston rings in a single ring groovewith their gaps circumferentially spaced from one another. However,during operation of the piston, the piston rings may move independentlyof one another and their gaps thereafter become aligned. When thisoccurs, the compression gases may escape axially through the alignedgaps.

The plastic piston ring 61 retains the circumferential misalignment ofsuch rings. As illustrated in FIG. 6, the ring 61 is placed radiallyinwardly of two conventional compression rings 67 and 68. The radiallyouter face 65 of the ring 61 abuts the inner diameter faces 69 of thecompression rings 67 and 68. Because the ring 61 is made of a plasticmaterial, portions of its outer diameter face 65 will extrude into thegaps 70 as illustrated in FIG. 3. The extrusion points 71 will lock thering gaps 70 in circumferential misalignment and thereafter the pistonrings 67 and 68 and the ring 61 will move in the groove 72 as a unit.

The ring 61 further acts to prevent compression gas blowby through thering groove 72. As high-pressure gas enters the ring groove 72, asillustrated by the arrows 73, it will be trapped in the upper portion ofthe groove 72 by the ring 61. As the high-pressure gases contact thering, they will enter the groove 62 acting against the radially innerportion 75 to force the inner diameter walls 76 and 77 against thebackwall 78 of the ring groove. At the same time, they will increase thecircumferential expansion force of the outer diameter wall 65 againstthe inner diameters 69 of the rings 67 and 68. Due to the provision ofthe three grooves 62, 63 and 64, the ring 61 is slightly compressible inboth an axially downward and radially inward direction. Further, thepresence of high-pressure gas in the groove 62 will force apart theradially inner portion 75 and the radially outer portion 79 of the ring61 thereby creating both the sealing force against the backwall 79 andthe expansion force against the compression rings 67 and 68. ln thismanner, the gas will be trapped in the ring groove. An additionalfeature is provided by grooving both the top and the bottom axial endsof the ring 61 in that the ring may be insorted in the ring groove witheither of the grooves 62 or 63 on the top.

FIGS. 7 and 9 illustrate another modification of the ring of thisinvention which is inserted in an especially cut ring groove. The ring90 has an outer diameter face 91 adapted to contact the cylinder borewall, thereby providing an oil scraping lip.

The ring has a radially inner axially extending portion 93 which isintegral with a radially outer portion 94 through the radially extendingbottom portion 95. A groove 96 extending into the ring from the topthereof separates the inner portion 93 from the outer portion 94. Thetop 97 of the radially outer portion at the front face 91 is below thetop 98 of the radially inner portion and the axial top surface of theradially outer portion 94 has an arcuate slope from the point 97 to thegroove 96. The bottom 99 of the ring extends radially outward from thebackwall 100 to a point 101 beyond the groove 96. Thereafter, the bottomtapers arcuately axially downward and outward to the front face 91 sothat the bottom portion of the radially outermost portion 94 extendsaxially beyond and below the remainder of the ring. The scraping face 91is tapered radially inward from the bottom 102 to the top 97 thereof.

The piston groove 105 is a rectangular groove having a height slightlygreater than the height of the radially inner portion 93 of the ring 90.A secondary stacked portion 106 of the groove 105 receives the axiallyextended bottom portion of the radially outer portion 94. The portion106 of the groove is arcuately cut from the bottom 107 of therectangular groove at the outer diameter thereof. The portion 106 is cutradially into the piston a distance slightly less than the thickness ofthe lip portion 108 of the ring formed by the bottom of the radiallyouter portion 94. In this manner, the portion 108 projects out of thering groove to a point where it may contact the cylinder wall.

The backwall 100 of the ring 90 preferably bottoms against the backwall100a of the ring groove 105 in a manner substantially the same as thering 31 of FIG. 8.

When high-pressure compression gases flow into the ring groove 105 asillustrated by the arrow 109, they will encounter the groove 96 wherethey will press the face 91 against the cylinder wall. The taper of theface 91 allows the axially upper portion of the ring of be expandedagainst the cylinder wall when high-pressure gases are present in thegroove 96. The pressure of the compression gases will also act in thegroove 96 of the ring 90 to radially expand the same whereby thebackwall 100 of the ring 90 will be forced into sealing engagement withthe backwall 100a of the ring groove 105. The con tact between thecylinder wall and the axially lower portion of the scraping face 91allows the ring to function as an oil-scraping ring. The presence ofhigh-pressure gases in the groove 96 will increase the contact pressurebetween the face 91 of the ring 90 and the cylinder wall. As thepressure in the groove 96 increases, the portion of the front face 91 ofthe ring 90 contacting the cylinder wall will increase as the ring 90 iscircumferentially expanded. ln this manner the ring 90 functions as ananti-blowby ring in that it seals escape paths through the ring groove105 by contact with the axial end walls of the ring groove 105 and bysealing engagement with the backwall 100a of the groove. Further blowbybetween the piston head and the cylinder wall is minimized due toexpansion pressure con tact between the outer diameter face 911 of thering 90 and the cylinder wall. In order to aid in effectuating thisseal, the ring groove 105 is preferably equal to or just slightlygreater than the height of the inner diameter portion 93 of the ringgroove 90 so that the top thereof 98 may contact the axial end of thering groove in response to the pressure of gases in the groove 96 whenthe backwall 100 of the ring 90 is bottomed against the backwall 100a ofthe ring groove.

FIGS. 10 through 13 illustrate another embodiment of the plastic pistonring of this invention. FIG. 10 illustrates the ring received in aspecial top ring groove 121 in a piston 122. A portion of the ring ridesagainst the cylinder wall 123.

The ring 120 is an annular continuous plastic piston ring having a flatbottom or axial end 124 and a straight axially extending backwall 125.An axially extending groove 126b projects into the ring from the top 127thereof, dividing the ring into a radially inner portion 128 and aradially outer portion 129. The radially outer portion 129 terminates atits outer diameter with a cylinder wall engaging portion 130. The axialtop end 131 of the radially outer portion 129 is below the top 127 ofthe radially inner portion 128 and is spaced from the top sidewall 132of the piston groove 121. The axial height of the ring 120 at theradially inner portion is approximately the same as the height of thegroove. In this manner, the upper portion of the radially outer portionserves as a sealing lip with the bottom axial portion thereof cut backas at 134 to a reduced diameter portion so that the cylinder engagingportion 130 projects radially beyond the remainder of the ring.

The groove 121 is in close-spaced relation to the top 135 of the piston122 and is located above the normal position of the top ring groove 136of a standard piston. The ring 120 serves as an anti-blowby ringreducing harmful exhaust emissions as well as preventing entrance ofuncombusted fuel and oxygen mixtures into the space between the cylinderwall 123 and the piston 122 where they would normally not be combusteddue to the smallness of the area.

In addition, the ring acts in the same manner as previously describedrings. As high-pressure combustion gases force their way between the topof the piston and the cylinder wall, they are entrapped in the groove126 as indicated by the arrow 138. Their effect upon the groove will beto force the inner diameter portion 128 tightly against the back 139 ofthe piston groove and to force the bottom wall 124 of the ring againstthe bottom wall 140 of the groove, thereby preventing escape of gasesaround the ring in the groove. Further, they will force the cylinderwall engaging portion 130 of the outer diameter portion 129 tighteragainst the cylinder wall 123 thereby cutting off the flow at the outerdiameter. ln the absence of high-pressure gases in the groove 126, thecontact between the ring and the cylinder wall will be less therebyreducing friction. Therefore, contact between the cylinder wipingportion 130 and the cylinder wall 123 will be greatest during the powerand compression strokes and smallest during the intake stroke. Duringthe exhaust stroke, there will be a slight expansion effect on the ring.

FIG. 13 illustrates a dual ring, dual groove arrangement where one ofthe rings 150 identical to the ring 120 is inserted in a top groove 151identical to the groove 121. A secondary ring 152 which may be identicalto the rings 150 and 120, or which may be as illustrated having ashallower groove 154, is inserted in a lower ring groove 153. This ringacts as an oil control ring with the cylinder engaging lip 155 actingagainst the cylinder wall 156 to wipe excess oil therefrom and toprevent excess amounts of oil from being forced upwardly to the upperreaches of the cylinder where they could be combusted to formhydrocarbon deposits on the cylinder wall.

FIG. 14 illustrates a single ring 158 received in a wider top pistonring groove 159. The single ring 158 functions as a combination of therings 150 and 152 and has two axially spaced cylinder engaging lips 160and 161 separated by a reduced diameter portion 162 which does notnormally contact the cylinder wall. In this embodiment, the lower lip161 functions as an oil control lip while the upper lip 160 functions inthe manner of the cylinder engaging portion 130 of the ring 120.

It can therefore be seen from the above that our invention provides animproved plastic piston ring which reduces the exhaustion of harmfulinternal combustion engine emission products by reducing gas blowbybetween the piston and the wall of the cylinder in which the pistonoperates. In some embodiments, the ring is placed behind a standardcombustion ring or ring set and transforms the axially directed flowforce of the combustion gases into a radial pressure which seals theinterior of the piston ring groove to prevent gas blowby therethroughand which also increases the sealing contract between the compressionring and the cylinder wall. In other embodiments, the ring can directlyengage the cylinder wall with a given standard pressure and in thepresence of highpressure gases will contact the cylinder wall with agreater pressure while at the same time sealing the groove in which itis received to prevent internal groove blowby.

Although the teachings of our invention have herein been discussed withreference (6 specific theories and embodiments, it is to be understoodthat these are by way of illustration only and that others may wish toutilize may invention in different designs or applications.

We claim as our invention:

1. A piston and piston ring combination for use in internal combustionengines comprising a piston having a plurality of ring grooves therein,a plurality of piston rings in said grooves, at least one of said pistonrings having its inner diameter spaced from the inner diameter of a ringgroove, a plastic piston ring positioned radially interiorly of saidpiston ring in the groove, said plastic piston ring comprising anannular ring of plastic material having inner and outer diameters and anaxial thickness, an axially extending groove extending into said plasticpiston ring from the top thereof, said axial groove terminating inspaced relation to the bottom of the said plastic piston ring, saidgroove dividing said ring into radially inner and radially outerspaced-apart portions in the area of the axial groove, the outerdiameter of the radially outer portion abutting the inner diameter ofthe said one piston ring, the radially outer portion of the said plasticpiston ring having an axial height less than the axial height of thesaid ring groove, and the said radially outer portion movable withrespect to the radially inner portion in dependent response to thepresence of a high pressure in the said axial groove.

2. The combination of claim 1 wherein the said plastic piston ring is a360 continuous ring.

3. The combination of claim 2 wherein the said plastic piston ring isconstructed of a polyimide resin which is structurally stable at atemperature greater than 500 F.

4. A piston and piston ring combination for use in internal combustionengines comprising: a piston, at least one ring groove in said piston,said ring groove having a metal split piston ring received therein, saidmetal piston ring having an axial height less than the height of thering groove, a plastic piston ring concentric with said metal ringgroove, a plastic piston ring concentric with said metal ring receivedin said ring groove radially interiorly of said metal ring, said plasticpiston ring being substantially U-shaped in cross section with theopening of the U extending upwardly, the outer diameter leg of the saidU having an axial height less than the axial height of the ring groove,the inner diameter leg of the said U having an axial height greater thanthe outer diameter leg, said plastic piston ring bottomed in the saidring groove, the radially outer leg of the plastic piston ringcircumferentially contacting the inner diameter of the said metal pistonring and the said radially outer leg movable with respect to the saidradially inner leg in dependent response to the presence of pressure inthe opening of the said U-shaped ring, whereby high-pressure gasesentering the ring groove above the said metal piston ring will enter thesaid opening and press the inner diameter leg into sealing engagementwith the bottom of the ring groove and the outer diameter leg intosealing engagement with the inner diameter of the metal piston ringthereby entrapping the said gas in the said ring groove.

5. The combination of claim 4 wherein the outer diameter of the saidplastic piston ring is circumferentially curved in an axial direction.

6. The combination of claim 4 wherein the outer diameter of the saidplastic piston ring is circumferentially tapered in an axial direction.

7. The combination of claim 4 wherein the inner diameter of the saidplastic piston ring is axially tapered.

8. The combination of claim 4 wherein the inner diameter of said plasticpiston ring is axially curved.

9. A piston and piston ring combination for use in internal combustionengines comprising: a piston having at least one ring groove therein, aplurality of axially thin split annulus piston rings received in saidgroove projecting radially beyond said groove, said piston ringspositioned one atop the other in said groove, the inner diameters ofsaid piston rings terminating in spaced relationship to the bottom ofsaid groove, a plastic piston ring received in said groove radiallyinwardly of said metal piston ring, the said plastic piston ring havingits inner diameter bottomed on the bottom of the ring groove and itsouter diameter contacting the inner diameters of the said metal pistonrings, an axially extending groove projecting into the said plasticpiston ring intermediate the inner and outer diameters thereof, the saidaxial groove projecting into the said ring from the top axial endthereof and terminating in spaced relationship to the bottom axial endthereof, the said plastic piston ring resilient whereby the outerdiameter is movable with respect to the inner diameter in dependentresponse to the presence of high pressure fluid in the said axialgroove.

10. The combination of claim 9 wherein portions of the material of thesaid plastic piston ring extend from its outer diameter into the gaps inthe split annulus metal rings, the said gaps being circumferentiallyspaced from one another whereby the said metal rings are restrainedagainst independent rotation with respect to one another.

11. The combination of claim 10 wherein the said plastic piston ring isa 360 continuous ring constructed of a hightemperature plastic.

12. The combination of claim 10 wherein the plastic piston ring has aradial groove in the ring from its inner diameter, the said ring groovepositioned intermediate the axial ends of the said plastic piston ring.

13. The combination of claim 12 wherein the said plastic iii piston ringhas a second axial extending groove positioned intermediate the innerand outer diameters thereof extending into the ring from the bottomaxial end thereof and the said radial groove and axial groove bottom inspaced relationship from one another.

114. in an internal combustion engine having at least one pistonreciprocatingly positioned in a cylinder, the piston having ring groovestherearound with metal piston rings therein, the improvement of at leastone of said grooves having a plastic piston ring received thereinpositioned radially interiorly of the metal piston ring, said plasticpiston ring being resilient and having a pressure-receiving axial groovetherein, the plastic piston ring being responsive to the presence ofpressures in said ring groove radially behind the said metal ring bysealing contact between the plastic piston ring and the backwall of thering groove and inner diameter of the metal ring.

1. A piston and piston ring combination for use in internal combustion engines comprising a piston having a plurality of ring grooves therein, a plurality of piston rings in said grooves, at least one of said piston rings having its inner diameter spaced from the inner diameter of a ring groove, a plastic piston ring positioned radially interiorly of said piston ring in the groove, said plastic piston ring comprising an annular ring of plastic material having inner and outer diameters and an axial thickness, an axially extending groove extending into said plastic piston ring from the top thereof, said axial groove terminating in spaced relation to the bottom of the said plastic piston ring, said groove dividing said ring into radially inner and radially outer spaced-apart portions in the area of the axial groove, the outer diameter of the radially outer portion abutting the inner diameter of the said one piston ring, the radially outer portion of the said plastic piston ring having an axial height less than the axial height of the said ring groove, and the said radially outer portion movable with respect to the radially inner portion in dependent response to the presence of a high pressure in the said axial groove.
 2. The combination of claim 1 wherein the said plastic piston ring is a 360* continuous ring.
 3. The combination of claim 2 wherein the said plastic piston ring is Constructed of a polyimide resin which is structurally stable at a temperature greater than 500* F.
 4. A piston and piston ring combination for use in internal combustion engines comprising: a piston, at least one ring groove in said piston, said ring groove having a metal split piston ring received therein, said metal piston ring having an axial height less than the height of the ring groove, a plastic piston ring concentric with said metal ring groove, a plastic piston ring concentric with said metal ring received in said ring groove radially interiorly of said metal ring, said plastic piston ring being substantially U-shaped in cross section with the opening of the U extending upwardly, the outer diameter leg of the said U having an axial height less than the axial height of the ring groove, the inner diameter leg of the said U having an axial height greater than the outer diameter leg, said plastic piston ring bottomed in the said ring groove, the radially outer leg of the plastic piston ring circumferentially contacting the inner diameter of the said metal piston ring and the said radially outer leg movable with respect to the said radially inner leg in dependent response to the presence of pressure in the opening of the said U-shaped ring, whereby high-pressure gases entering the ring groove above the said metal piston ring will enter the said opening and press the inner diameter leg into sealing engagement with the bottom of the ring groove and the outer diameter leg into sealing engagement with the inner diameter of the metal piston ring thereby entrapping the said gas in the said ring groove.
 5. The combination of claim 4 wherein the outer diameter of the said plastic piston ring is circumferentially curved in an axial direction.
 6. The combination of claim 4 wherein the outer diameter of the said plastic piston ring is circumferentially tapered in an axial direction.
 7. The combination of claim 4 wherein the inner diameter of the said plastic piston ring is axially tapered.
 8. The combination of claim 4 wherein the inner diameter of said plastic piston ring is axially curved.
 9. A piston and piston ring combination for use in internal combustion engines comprising: a piston having at least one ring groove therein, a plurality of axially thin split annulus piston rings received in said groove projecting radially beyond said groove, said piston rings positioned one atop the other in said groove, the inner diameters of said piston rings terminating in spaced relationship to the bottom of said groove, a plastic piston ring received in said groove radially inwardly of said metal piston ring, the said plastic piston ring having its inner diameter bottomed on the bottom of the ring groove and its outer diameter contacting the inner diameters of the said metal piston rings, an axially extending groove projecting into the said plastic piston ring intermediate the inner and outer diameters thereof, the said axial groove projecting into the said ring from the top axial end thereof and terminating in spaced relationship to the bottom axial end thereof, the said plastic piston ring resilient whereby the outer diameter is movable with respect to the inner diameter in dependent response to the presence of high pressure fluid in the said axial groove.
 10. The combination of claim 9 wherein portions of the material of the said plastic piston ring extend from its outer diameter into the gaps in the split annulus metal rings, the said gaps being circumferentially spaced from one another whereby the said metal rings are restrained against independent rotation with respect to one another.
 11. The combination of claim 10 wherein the said plastic piston ring is a 360* continuous ring constructed of a high-temperature plastic.
 12. The combination of claim 10 wherein the plastic piston ring has a radial groove in the ring from its inner diameter, the said ring groove positioned intermediate the axial ends of the said plastic piston ring.
 13. The combination of claim 12 wherein the said plastic piston ring has a second axial extending groove positioned intermediate the inner and outer diameters thereof extending into the ring from the bottom axial end thereof and the said radial groove and axial groove bottom in spaced relationship from one another.
 14. In an internal combustion engine having at least one piston reciprocatingly positioned in a cylinder, the piston having ring grooves therearound with metal piston rings therein, the improvement of at least one of said grooves having a plastic piston ring received therein positioned radially interiorly of the metal piston ring, said plastic piston ring being resilient and having a pressure-receiving axial groove therein, the plastic piston ring being responsive to the presence of pressures in said ring groove radially behind the said metal ring by sealing contact between the plastic piston ring and the backwall of the ring groove and inner diameter of the metal ring. 